Cork asbestos elastomer sheet



United States Patent 71cc.

CORK ASBESTOS ELASTOMER SHEET Stephen M. Lillis and John C. Toman,Chicago, III., assignors to Victor Manufacturing & Gasket Co., Chicago,11]., a corporation of lllinois No Drawing. Application August 28, 1953,Serial No. 377,256

1 Claim. (Cl. 92-3) This invention relates to fibrous compositions forforming gaskets and has for its principal object the provision of a newand improved composition of this kind.

It is a main object of the invention to provide a fibrous formed upon awet lap cylinder paper making machine into fibrous sheets from whichgaskets can be cut.

,Another object of the invention is to provide a gasket material thatcan be manufactured at low cost without sacrificing quality.

.Further objects of the invention not specifically mentioned here willbe apparent from the description and claim which follow.

.Many parts of internal combustion engines, such as crankcase pans,rocker arm covers and valve covers, are manufactured of relatively thinmetal and must be tightly sealed against the parts with which they areregistered with relatively low sealing pressures. Gaskets made of corkhave functioned well for these purposes because the compressibility andrecovery characteristics of cork permitted the formation of fluid tightseals by application of relatively low pressures between the parts.

.With the advent of high compression engines and pressurized coolingsystems, crankcase oils are raised to higher temperatures than formerly,temperatures which have a deleterious elfect upon cork, with the resultthat a better gasketingmaterial capable of withstanding highertemperatures is highly desirous, if not absolutely necessary.

For a number of years, gasketing material has been made by combiningwith asbestos fibers an elastomer binder which is impervious to oils,greases and coolants, and is capable of withstanding the'tempe raturesnow encountered. Such materials are, however, relatively incompressiblewhen compared with cork, and consequently higher sealing pressures arerequired to form a fluid tight seal between the engine parts. This facteliminates gaskets composed of such material from use in the sealing ofcrankcase pans, rocker arm covers and valve covers wherein, because ofthe light gauge metals used, it is difficult to establish and maintainsealing pressures high enough to form a satisfactory seal.

In the prior art of which we are aware, are numerous materials formed ofasbestos fibers and elastomer and cork, in effort to secure a greatercompressibility and recovery while maintaining the temperature andimpervious characteristics of asbestos and elastomer.

Cork, one of the lightest of natural materials having a specific gravityof from .15 to .20, contains a myriad of microscopic air-filled cellswhich aggregate more than 50% of the volume of the cork. It is becauseof these aircells that the characteristics of low gravity, highcompressibility and recovery, low thermal conductivity and low fluidadsorption because of lack of capillarity, are obtained.

Merely grinding cork to fine particle size and incorporating the groundmaterial in the mix from which the fibrous sheet is made presentsproblems. If the particle size is small, as in the range of 200 mesh, asin the case of certain prior art compositions of which we are aware,much of the resiliency of the cork is lost through the destruction ofthe microscopic air cells, and cork in the composition serves mainly, ifnot entirely, as an organic filler. Gaskets made from such material showvirtually no improvement 'in the characteristics of compressibility andrecovery.v On the other hand, attempts to incorporate large particlesize cork into such compositions present the difliculty of evendistribution of cork particles throughout the sheet because of thetendency of cork to float to the top of the slurry from which the sheetis made. To form a gasketing material in which the distribution. of corkparticles is uneven, obviously cannot resultina satisfactory gasketsince it would be highly compressible at points and lack compressibilityelsewhere.

, The present invention seeks to form, on an ordinary Wet lap cylinderpaper making machine, a fibrous asbestos, cork andelastomer material inwhich sufficient cork is incorporated in a uniform manner to add desiredcompressibility and recovery'characteristics to the material withoutunduly lowering the ability of the material to withstand hightemperatures.

-To accomplish this end, we prefer to employ cork ground to such aparticle size as to pass through a 40- mesh screen and to beretainedupon a SO-mesh screen, that is, to employ ground cork having aminimum particle-size of 50 mesh. In the mixing of the ingredients fromwhich our improved material is made, sufficient wet ting agent isemployed to adequately wet the cork particles thereby to maintain themsuspended within the slurry delivered to the cylinder of the machine,with the result that these cork particles are distributed through thesheet in a very uniform manner and the physical characteristics of thesheet so formed render it satisfactory for use as a gasketing materialwhere low pressures and high tempcratures are involved. While thepresence of cork in the composition lowers the temperaturecharacteristics of the composition, since cork is less capable ofwithstanding high temperatures than are the asbestos and elastomeringredients, proper proportioning of the ingredients results in afibrous sheet material havingvtemperature characteristics satisfactoryfor the uses intended.

In the preparation of a preferred form of our improved composition, 450gallons of water are placed in the beater of a paper making machine, and175 pounds of virgin asbestos fiber and 25 pounds of refiberized scrapasbestos material, together with pounds of cork ground to SO-meshminimum, are added. The beater is started and 2 pounds of sodiumhexametaphosphate are added to soften the water and thereby aid inthoroughly wetting the asbestos fibers and cork. Ordinarily thispreliminary beating operation is continued for about five minutes.

Sixty (60) pounds of a curative material are then added to the mix.Preferably this curative material consists of 43.2 pounds of water, 4pounds of a curing agent such as zinc oxide, .8 of a pound of anaccelerator such as sulfur, 1.6 pounds of an anti-oxidant such asphenyl-beta-naphthylamine, 8 pounds of a filler such as easy processingchannel carbon black, .8 of a pound of a wetting agent such as aralkylpolyether alcohol, .8 of a pound of a filler and stabilizer such asbentonite, and .8 of a pound of accelerator such as thiocarbanilide.This blend of ma- Patented July 16, 1957' terials is allowed to mix foran additional five minutes, f r which 2 .0 pounds of neoprene latexcontaining 35% solids and adjusted to a pH of 8 by the addition ofpounds of 5% acetic acid, together with 160 pounds of disp r ng agent,pre rably containing 152 pounds of.

water and 8. pounds of sodium .alk-yl a y .s f n are added, togetherwith sufficient Water to bring the volume of the mix i th b ate up to900 gallo s- The heater is operated for approximately five minutes uri gwhic 3 pounds f p per mak r a m s slowly added to the mixture to aid incoagulating the rubber onto the fiber and cork. When all of the rubberhas been so coagulated, the water will be clear, thereby indicating hple on of the batch.

The mix ur o prepared is diluted to. a slurry of proper solids contentfor the, machine upon which it is to be formed into a sheet. In oneinstance a slurry of 1% lids content has been found to be satisfactory.The wet lap cylinder paper forming machine is operated to form from thisslurry a Sheet, of the desired thickness and when that thickness hasbeen achieved the sheet is removed, air-dried preliminarily, and thenoven-dried down to a final low moisture content to complete theformation of the sheet.

In a wet lap cylinder type paper machine, the fibers in the slurry arepicked up on a belt and transferred from it to the cylinder of themachine to build up on that cylinder a sheet or web of desiredthickness. The fibers are laid in the sheet in strata or layers and thelayers held together by the interlacing of the fibers in the layers.With the thorough wetting of the cork particles, achieved through theabove formula, the tendency .of the particles to float to the top of theslurry is minimized to such an extent that with the proportions of corkparticles employed the distribution of those particles in the sheet issutficiently uniform to render the sheet entirely satisfactory for thepurposes intended. Thus we are able to obtain the advantages incompressibility and recovery resulting from the use of larger particlesof cork without sacrificing uniformity of distribution of thoseparticles in the sheet.

Gaskets formed from such material, when tested in accordance with theAmerican Society for Testing Materials specifications D-1147-51T andD1l7051T, have been found to have a tensile strength of 500 pounds tothe square inch, a compressibility of 35% plus or minus 5%, and arecovery of 40% minimum. The prior art composition of asbestos andneoprene, when tested under the same conditions, has a tensile strengthof 1000 pounds to the square inch, a compressibility of 25% plus orminus 5%, and a minimum recovery of 40%. Thus it will be seen thatthrough the sacrifice of 500 pounds of tensile strength, a gain of 40%over the compressibility is achieved by the addition of the cork.Recovery which amounts to 40% of the compressibility is likewisesubstantially increased by the addition of the cork, althoughpercentagewise it remains unchanged. This recovery compares favorablywith that of cork composition.

Temperaturewise our new composition shows substantial improvement overcork. Under continuous operation our asbestos cork neoprene compositionwill withstand 300 F. without deterioration and for intermittent service350 F. This compares favorably with the 300 F. continuous rating of theasbestos neoprene composition and with its 400 F. intermittent rating.For even higher temperatures, polyacrylates elastomer may be used toraise the temperature characteristic to 350 F. in continuous operationand 500 F. in intermittent operation. While such temperatures are belowthose which the polyacrylate rubber is capable of withstanding, that isto be expected, since cork of itself is wholly incapable of withstandingsuch temperatures and its inclusion in the mixture must necessarilylower the maximum temperature to which the material may safely besubjected.

Our improved material is impervious to oils, greases and coolants to thesame degree as are prior asbestos neoprene compositions and is entirelysatisfactory for the purposes intended. The cost of manufacture is low.

While We have illustrated our composition by describing a preferredembodiment of it, we have done so by way of example only, as there aremany modifications which can be made by one Skilled in the art withinthe teachings of the invention.

Having thus complied with the statutes by describing a preferredembodiment of our invention, what we consider new and desire to haveprotected by Letters Patent is pointed out in the appended claim.

What is claimed is:

A fibrous sheet of material suitable for use in the formation of gasketsand containing the residue after drying from a slurry formed with 175pounds of virgin asbestos fiber, pounds of refiberized scrap asbestos,100 pounds of ground cork of 50 mesh minimum particle size, 2 pounds ofsodium hexametaphosphate, 4 pounds of zinc oxide, .8 pound of sulfur,1.6 pounds of phenyl-betanaphthylamine, 8 pounds of carbon black, .8pound of aralkyl polyether alcohol, .8 pound of bentonite, .8 pound ofthiocarbanilide, 240 pounds of neoprene latex containing 35% solids, 5pounds of 5% acetic acid, together with 160 pounds of dispersing agent,containing 152 pounds of water and 8 pounds of sodium alkyl arylsulfonate, pounds of paper makers alum, together with sufficient Waterto effect complete coagulation of the neoprene on the fibers and toreduce the solids content of the slurry to the range of 1%, whichmaterial has a tensile strength of 500 pounds per square inch, acompressibility of and a recovery of minimum, and is capable ofwithstanding temperatures of 300 F. in continuous service and 350 F. inintermittent service without deterioration.

References Cited in the file of this patent UNITED STATES PATENTS1,785,357 Levin Dec. 16, 1930 2,550,143 Eger Apr. 24, 1951 2,584,959Yocom et a1. Feb. 5, 1952 2,613,190 Feigley Oct. 7, 1952

